Purification of acrylonitrile



PURIFICATION OF ACRYLONITRILE Marcel Borrel, Pierre-Benite, France, assignor to Societe Industrielle des Derives delAc'etylene (S. I. D. A.), Paris, France, a corporation of France No Drawing. Application May 5, 1955,

Serial No. 506,390 1 Claims priority, application France May 19,1954

8 Claims. (Cl. 202-57) The present invention relates to the purification of acrylonitrile.

It is known that acrylonitrile, and especially that which is obtained by the combination of acetylene with hydrocyanic acid in the presence of a catalyst, contains in the unrefined state impurities of various kinds.

The most troublesome of these impurities are the dienic compounds, that is to say the compounds comprising two double carbon-carbon links in the position a. In the first place, some of these compounds, by reason of their physical and chemical characteristics, are particularly diflicult to separate from the acrylonitrile. On the other hand, the dienic compounds, even when they are only present as traces, affect the properties of the polymers manufactured from acrylonitrile, tending in particular to make them insoluble.

Amongst the dienic compounds, it is more particularly divinyl-acetylene and cyano-butadiene 1.1.3. which are concerned.

The present invention relates to a particularly simple and effective method of destroying these dienic compounds.

. of dienes so that the production of heat does not result in a troublesome increase in temperature.

A After the nitrogen tetroxide has been introduced, it is' preferable to Wait fora certain-time, for example minutes to one hour, in order to give the reaction time to complete itself.,The purified acrylonitrile [can then be separated out by distillation. 1 i

The acidity which is produced by the reaction may be neutralised before the distillation process. Although this operation is not absolutely essentail, it maybe desirable from the point of view of corrosion.

This method consists in acting upon the acrylonitrile to be purified with nitrogen tetroxide, using a quantity calculated to destroy the dienic impurities; the .acrylonitrile is then separated by distillation from the mixture thus obtained.

It is already known that nitrogen tetroxide, having the formula N204, may be added to the double carboncarbon links, giving, furthermore, fairly complex mixtures. On the other hand, it could not in any way be forseen that it was possible, by the action of nitrogen tetroxide, to destroy the dienes up to the last traces, whilst leaving the acrylonitrile practically unaffected.

The method of carrying the invention into efi'ect is particularly simple. It is sufiicientto introduce the necessary quantity of nitrogen tetroxide, either in the gaseous form or as a liquid, under the surface of the acrylonitrile at ambient temperature. The operation may be efiected either on successive charges of acrylonitrile contained for example in a tank provided with an agitator or in a continuous manner by introducing the nitrogen tetroxide into a flow of acrylonitrile. The quantity of'nitrogen tetroxide to be used will depend naturally upon the quantity of impurities contained in the acrylonitrile; if the quantity introduced is greater than that which is exactly required, the supplement will react with the acrylonitrile, but ithas been found that it is useless to add any appreciable excess of reagent and that, by addin the quantity of nitrogen tetroxide which is proportional to the quantity of dienes, the latter are completely destroyed without affecting the acrylonitrile.

The great affinity of nitrogen tetroxide for dienes is clearly shown by the production of heat which takes place as soon as the reagent is introduced. It may be necessary to cool the locality in which the reaction takes place, but in practice, the operations are confined to a medium which contains as a maximum only a small percentage It is an advantage to separate out the acrylonitrile by carrying it away with steam. On the one hand, there is thus obtained with good efiiciency an acrylonitrile which is particularly pure and which only requires to be dried. On the other hand, the reaction products of the nitrogen tetroxide which remain in the end reactions are liable to be decomposed more or less violently if they are overheated after they have been concentrated by the distillation of the acrylonitrile.

The examples given below will emphasize the remarkable results obtained by the use of the invention.

Example 1 In a vessel provided with an agitator and a thermometer, there were placed 200 grams of acrylic nitrile containing 0.64% by weight of divinyl-acetylene to which there was introduced for a period of 20 minutes 3 grams of nitrogen tetroxide in liquid form and having a degree of purity of 99.5%. During this introduction, the vessel was cooled by a current of water at 15C. The reaction was then allowed to proceed for half an hour, the acrylonitrile being then separated out from the products formed by carrying it away with steam. After decantation and drying of the acrylic nitrile, analysis showed that it contained less than 0.0003% by weight of divinylacetylene.

Example 2 When treated under the same conditions as in Example 1, but with only 2 grams of nitrogen tetroxide, the acrylic nitrile, which initially contained 0.64% of divinyl-acetylene, only contained 0.022% by Weight.

Example 3 divinyl-acetylene and less than 0.001% of cyano-butadiene.

What we claim is:

l. A method of purifying acrylonitrile from dienic compounds contained therein, comprising the step of reacting said acrylonitrile with nitrogen peroxide in quantity sufficient to destroy said dienic'impurities, whereafter the acrylonitrile is separated out by distillation.

2. A method of purifying acrylonitrilefrom ,dienic compounds contained therein, .comprising the step of re acting said acrylonitrile with nitrogen peroxide in quantity sufficient to destroy said dienic impurities, whereafter the acrylonitrile is drawn off by steam.

3. method of purifying acrylonitrile from dienic compounds contained therein, comprising the step of introducing nitrogen tetroxide below the surface of said acrylonitrile, in quantity sufficient to destroy said dienic impurities, whereafter the acrylonitrile is separated out by distillation.

4. A method as claimed in claim 3, in which liquid nitrogen tetroxide is used.

5. A method as claimed in claim 3, in which gaseous nitrogen tetroxide is used.

6. A method of purifying acrylonitrile from dienic compounds contained therein, comprising the steps of reacting said acrylonitrile with nitrogen peroxide in quantity suflicient to destroy said dienic impurities, and neutralising the reaction mixture, whereafter the acrylonitrile is separated out by distillation.

7. A method of purifying acrylonitrile from dienic compounds contained therein, comprising the steps of reacting said acrylonitrile with nitrogen peroxide in quantity suflicient to destroy said dienic impurities, and leaving the reaction mixture at rest during about 15 to 60 minutes, Whereafter the acrylonitrile is separated out by distillation.

8. A method of purifying acrylonitrile from dienic References Cited in the file of this patent UNITED STATES PATENTS 2,255,421 Groll Sept. 9, 1941 2,444,589 Bann a July 6, 1948 2,622,097 Osborne Dec. 16, 1952 2,684,978 Stehman July 27, 1954 2,719,169 De Croes' Sept. 27, 1955 

1. A METHOD OF PRUIFYING ACRYLONITRILE FROM DIENIC COMPOUNDS CONTAINED THEREIN, COMPRISING THE STEP OF REACTING SAID ACRYLONITRILE WITH NITROGEN PEROXIDE IN QUANTITY SUFFICIENT TO DESTROY SAID DIENIC IMPURITIES, WHEREAFTER THE ARCYLONITRILE IS SEPARATED OUT BY DISTILLATION. 